One of our site security daemons appears to get bad info from somewhere (Apache? UBBS? ??) and blocks addresses, and we've been unable to determine the exact cause or how to unblock a specific address. It happens to me often after I do something on the membership pages (approve, deny).
While I haven't done anything like that lately, this weekend I've been having problems when using the NIH VPN client to access the site. I can load the (cached) front page okay, but attempts to do anything else (view a forum, reload page) leads to a timeout. I was able to resolve this today by clearing charmm.org cookies and reconnecting (different IP), but that's not something I'd like to be doing routinely.
If your home address is relatively fixed (my home router address doesn't change very often), we can add it to a white list; contact Tim or me by email.